A new planet circling another star has been found using a new technique that will allow astronomers to find planets no other current method can.

Until now, planets around other stars were detected by the effect they have on their parent star, limiting the observations to large, Jupiter-like planets and those in very tight orbits.

The new method uses the patterns created in the dust surrounding a star to discern the presence of a planet that could be as small as Earth, or in an orbit so wide that it would take hundreds of years to observe its effect on its star using the conventional method.

"We're very excited because this will open up the possibility of finding planets that we'd probably never detect just looking at the parent star," says Dr Alice Quillen, Assistant Professor of Physics and Astronomy at the University of Rochester, New York State, US.

"We can confirm the presence of certain planets in five years instead of the two centuries it would otherwise take."

Epsilon Eridani C

The new planet was discovered orbiting the star Epsilon Eridani which is about 10 light-years from Earth. It is one of the lowest mass planets yet found around another star and has by far the longest, largest orbit of any yet seen.

Dust around Epsilon Eridani (James Clerk Maxwell)

Epsilon Eridani is a star that already has one discovered planet, the size of Jupiter, orbiting the star every five years or so.

By contrast, the new planet, tentatively named Epsilon Eridani C, is roughly a tenth of Jupiter's mass and completes an orbit once every 280 years.

Unlike current methods, Quillen's technique does not use direct light from the star, but rather light radiating from the dust surrounding it.

It is a method that does not work for all stars because not all stars have large concentrations of dust, but those that do, like Epsilon Eridani, can display certain telltale patterns in their dust fields that betray the existence of a planet.

Close match

Quillen used computer simulations of how a planet might swirl the dust surrounding a star. She found that for certain situations where the planet orbited the star three times for every two times the dust orbited, or five times for every three dust orbits, the dust would settle into definable clumps in a ring around the star.

After finding this pattern in her simulations, Quillen looked to see if she could find a star surrounded with dust with these patterns. She found Epsilon Eridani.

"The fact that the dust around this star closely matches what we expected to see if a planet were present doesn't mean we know for sure that a planet is really there," says Quillen.

"The images of Epsilon Eridani that we matched with our model are five years old. If Epsilon Eridani were re-observed then the clumps should have moved. The rate that they move will pin down the likely location of the planet."

Quillen plans to find more planets and work out new simulations to determine if patterns could emerge from other kinds of planetary orbits. She is hoping to find if a change in the light emitted from the dust fields could help signal the presence of a planet.